Temperature alert thresholds

I have been asked to set up tempertature alerting for our Cisco devices in our network closets.  Getting it set up has not been an issue and I have the alerts and reports built.  The only issue I am running into is what is the best practice alert threshold for Temperature alerts.  Any thoughts?

I am using a Universal poller and OID 1.3.6.1.4.1.9.9.13.1.3.1.3

Thanks.